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implemented Legendre

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orignal 2019-12-10 10:45:08 -05:00
parent 8d74905257
commit 7417867d0f
2 changed files with 75 additions and 44 deletions
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38
libi2pd/Elligator.cpp
View file

@ -40,8 +40,9 @@ namespace crypto
BN_free (u); BN_free (iu);
}
void Elligator2::Encode (const uint8_t * key, uint8_t * encoded) const
bool Elligator2::Encode (const uint8_t * key, uint8_t * encoded) const
{
bool ret = true;
BN_CTX * ctx = BN_CTX_new ();
BN_CTX_start (ctx);
@ -56,6 +57,12 @@ namespace crypto
BIGNUM * xA = BN_CTX_get (ctx); BN_add (xA, x, A); // x + A
BN_sub (xA, p, xA); // p - (x + A)
BIGNUM * uxxA = BN_CTX_get (ctx); // u*x*xA
BN_mod_mul (uxxA, u, x, p, ctx);
BN_mod_mul (uxxA, uxxA, xA, p, ctx);
if (Legendre (uxxA, ctx) != -1)
{
BIGNUM * r = BN_CTX_get (ctx);
BN_mod_inverse (r, xA, p, ctx);
BN_mod_mul (r, r, x, p, ctx);
@ -70,13 +77,18 @@ namespace crypto
encoded[i] = encoded[15 - i];
encoded[15 - i] = tmp;
}
}
else
ret = false;
BN_CTX_end (ctx);
BN_CTX_free (ctx);
return ret;
}
void Elligator2::Decode (const uint8_t * encoded, uint8_t * key) const
bool Elligator2::Decode (const uint8_t * encoded, uint8_t * key) const
{
bool ret = true;
BN_CTX * ctx = BN_CTX_new ();
BN_CTX_start (ctx);
@ -89,6 +101,8 @@ namespace crypto
BIGNUM * r = BN_CTX_get (ctx); BN_bin2bn (encoded1, 32, r);
if (BN_cmp (r, p12) < 0) // r < (p-1)/2
{
// v = -A/(1+u*r^2)
BIGNUM * v = BN_CTX_get (ctx); BN_mod_sqr (v, r, p, ctx);
BN_mod_mul (v, v, u, p, ctx);
@ -103,7 +117,7 @@ namespace crypto
BN_mod_mul (t, t, vpA, p, ctx);
BN_mod_add (t, t, v, p, ctx);
int legendre = 0; // TODO:
int legendre = Legendre (t, ctx);
BIGNUM * x = BN_CTX_get (ctx);
if (legendre == 1)
BN_copy (x, v);
@ -120,10 +134,14 @@ namespace crypto
key[i] = key[15 - i];
key[15 - i] = tmp;
}
}
else
ret = false;
BN_CTX_end (ctx);
BN_CTX_free (ctx);
return ret;
}
void Elligator2::SquareRoot (const BIGNUM * x, BIGNUM * r, BN_CTX * ctx) const
@ -140,6 +158,18 @@ namespace crypto
BN_sub (r, p, r);
}
int Elligator2::Legendre (const BIGNUM * a, BN_CTX * ctx) const
{
// assume a < p, so don't check for a % p = 0
BIGNUM * r = BN_CTX_get (ctx);
BN_mod_exp (r, a, p12, p, ctx); // r = a^((p-1)/2) mod p
if (BN_is_word(r, 1))
return 1;
else if (BN_is_zero(r))
return 0;
return -1;
}
static std::unique_ptr<Elligator2> g_Elligator;
std::unique_ptr<Elligator2>& GetElligator ()
{

5
libi2pd/Elligator.h
View file

@ -17,12 +17,13 @@ namespace crypto
Elligator2 ();
~Elligator2 ();
void Encode (const uint8_t * key, uint8_t * encoded) const;
void Decode (const uint8_t * encoded, uint8_t * key) const;
bool Encode (const uint8_t * key, uint8_t * encoded) const;
bool Decode (const uint8_t * encoded, uint8_t * key) const;
private:
void SquareRoot (const BIGNUM * x, BIGNUM * r, BN_CTX * ctx) const;
int Legendre (const BIGNUM * a, BN_CTX * ctx) const; // a/p
private: